Prior art systems are known in which the existence of a single resonant circuit in a detection field or zone is utilized as an anti-theft type apparatus. Essentially, if an article having a single resonant frequency tag passes through a detection zone, an alarm is generated which indicates the unauthorized presence of store goods in the detection zone. Such resonant circuits have been constructed in accordance with standard printed circuit board techniques. These systems do not identify which specific goods are in the detection zone since only a single code is used for tagging or identifying all tagged goods in a store inventory.
Some prior RF tagging systems have provided multiple different tuned (resonant) circuits on a tag so as to specifically identify the goods to which the tag is attached or the destination to which those goods should be directed. Such systems have been proposed for parcel or other article delivery systems wherein resonant circuits are utilized to provide a destination or sender code rather than printed bar codes.
The use of resonant circuit tagging is advantageous in that it is not subject to problems such as dirt obscuring a portion of a printed bar code and causing an error in determining the code associated with the article. Also, exact alignment of the tag with the detection system may not be required in RF tagging systems, since generally it is desired only to detect the presence of the resonant circuits somewhere in a broad detection zone. This can be achieved without precise alignment between the resonant circuit, the detection zone and the detection apparatus. However, prior systems utilizing multiple tuned circuit detection contemplate sequentially generating or gating each of the different resonant frequency signals to a transmitter antenna, and then waiting for reflected energy from each of the tuned circuits to be detected. Some frequency tagging systems look for absorption of RF energy by a resonant circuit during the transmission of each test frequency signal.
Generally, each different resonant frequency in a multiple frequency system is provided by a master oscillator circuit whose output is essentially swept or stepped to sequentially provide each desired output frequency. In all of these systems the result is essentially a slow detection system since the systems sequentially radiate each of the different frequencies. Rapid detection is achieved only if there are a few different frequencies involved. However, for complex coding which may require the use of up to 20 or more different frequencies, the overall system detection response is slow and may result in errors unless the tag throughput through the detection zone is intentionally slowed down. Since a major purpose of providing an RF tagging system is to improve the speed at which goods are handled by rapidly identifying the codes associated with the goods, this is undesirable.
Some prior RF tagging systems contemplate printing a large number of different resonant frequency circuits on a tag and then creating different codes by the selective adjustment of some of these resonant circuits. These systems have recognized that it may be necessary to adjust the resonant frequency provided for each circuit and such adjustment is generally contemplated as occurring by selective removal of metalizations forming the resonant circuit. Some systems have recognized that step adjustments of the resonant frequency of such tuned circuits is desirable and this has been implemented by punching holes of predetermined diameters in capacitive elements of the resonant circuit to thereby reduce capacitance and increase the frequency of the resonant circuit. Such known prior techniques are not readily adaptable to mass production of customized resonant frequency codes by a post factory manufacturing operation. Many times, the actual code to be utilized will not be known until immediately prior to attaching a tag or label to an article. In such a situation, an improved technique of adjusting the resonant frequencies of tuned circuits on a tag is desirable such that the process can be readily automated if desired or implemented even manually with a minimum amount of skill and precision required of the operator.
When it is possible to accurately control the orientation between the resonant multiple frequency tag and the detection system, some prior systems have noted that fewer different resonant frequencies may be needed to produce the desired end coding result. However, these prior systems accomplish this result by just limiting the number of circuits in the detection zone so that the zone can only accommodate a few different tuned circuits at one time. This has the undesirable effect of effectively requiring wide spacing between tuned circuits on a tag and therefore undesirably increasing the size of the tag on which the tuned circuits are provided.
Prior RF tags typically use etching to create desired metalization patterns, but this may not be readily adapted to mass production of such tags in a cost effective manner.